1. Field of the Invention
This invention relates to dynamic magnet systems, and more particularly to systems in which the linear motion of a magnet is used to generate electric power.
2. Description of the Related Art
Moving a magnet through a conductive coil induces a current flow in the coil. If the magnet is moved back and forth in a reciprocating motion, the direction of current flow in the coil will be reversed for each successive traverse, yielding an AC current.
Several electrical generating systems have been disclosed that make use of reciprocating magnet movement through one or more coils. For example, in various embodiments of U.S. Pat. No. 5,347,185, one, two or three rare earth magnets are positioned to move linearly back and forth relative to one or more coils. The magnets can either be fixed and the coil moved up and down relative to the magnet as by wave action, the coil can be fixed and the magnet moved relative to the coil as by pneumatic pressure, or the coil housing can be shaken or vibrated as by being carried by a jogger, all causing a reciprocating motion of a magnet which moves within the coil. In one embodiment four magnets are provided in successive polar opposition, with the two end magnets fixed and the middle magnets free to move back and forth along respective portions of a tube. The two middle magnets are separated from each other by the carrier for a middle coil, the carrier being approximately twice as wide as either of the middle magnets.
In U.S. Pat. No. 5,818,132, one embodiment discloses three moving magnets that are suspended within a vertical tube in polar opposition to each other and a pair of end magnets, with a number of coils spaced along the outside of the tube. To minimize friction between the moving magnets and the tube, the tube is oriented in a vertical position and moved up and down to move the magnets relative to the coils, thus generating currents in the coils. However, the vertical orientation interferes with the motion of the magnets, which have to fight gravitational forces to move relative to the tube. The coupling of tube movements into magnet motion, with a corresponding electrical output, is thus reduced.
The present invention provides a dynamic multiple magnet system which allows for an increased coupling between a support structure for the magnets and the motion imparted to the magnets themselves. This allows the support structure to be oriented for magnet movement in a primarily horizontal direction, thus greatly increasing the sensitivity of the device to applied motion.
These improvements are achieved by providing ultra low friction bearings between a plurality of magnets and a support structure, with the magnets arrange in polar opposition to each other. The critical angle of displacement for the magnets from a horizontal static position is less than 1 degree, and can be less than 10 minutes. The bearings are preferably implemented with a ferrofluid that establishes a static coefficient friction between the magnets and enclosure less than about 0.02. The ferrofluid preferably has a viscosity less than 10 centipoise, and in one embodiment comprises a light mineral oil medium mixed with isoparaffinic acid.
Rather than a single oscillation mode associated with a single magnet system, the multiple magnets have multiple oscillation modes that cause them to actively respond to numerous different types of applied support structure movements. Thus, electricity can be generated in response to random or semi-random movements, even when the movements are very gentle. Even numbers of moving magnets which move along a common axis can be used, with successive magnets kept apart only by their opposing magnetic polarities.
The dynamic magnet system can be used to power numerous operating systems, such as flashlights, cellular telephones, environmental sensors and emergency transmitters, either by powering the devices in real time or by charging associated batteries for the devices.
The invention further contemplates the use of one or more magnets that move relative to a support structure that has a ring-shaped axis. The magnets are oriented in polar opposition to move along the axis in response to support structure movements. Great sensitivity can be achieved when the orientation is primarily horizontal, as in a wave powered device that is floated on water or a wind powered device suspended in air.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.